3 weeks is really not much time - hydrolyzed collagen works slower than we'd like it to. Most people start noticing actual results between 2 to 3 months of daily use, and there are some factors that make a big difference - hydration, sleep, balanced diet, whether you're taking it with vitamin C (which helps with absorption). I know people who took almost 4 months to see real improvement in their hair and skin firmness, so it's pretty individual honestly.
The most important thing is to keep at it consistently, because stopping and starting again just ends up dragging out the results even longer. If after 2 months you haven't noticed anything, then yeah, it makes sense to reassess whether it's worth continuing for you.